The present invention relates to improved steerable electrode catheters having an irrigated tip.
Electrode catheters have been in common use in medical practice for many years. They are used to stimulate and map electrical activity in the heart and to ablate sites of aberrant electrical activity.
In use, the electrode catheter is inserted into a major vein or artery, e.g., femoral. artery, and then guided into the chamber of the heart which is of concern. Within the heart, the ability to control the exact position and orientation of the catheter tip is critical and largely determines how useful the catheter is.
In certain applications, it is desirable to have the ability to inject and/or withdraw fluid through the catheter. This is accomplished by means of an irrigated tip catheter. One such application is a cardiac ablation procedure for creating lesions which interrupt errant electrical pathways in the heart.
A typical ablation procedure involves the insertion of a catheter having a tip electrode at its distal end into a heart chamber. A reference electrode is provided, generally taped to the skin of the patient. RF (radio frequency) current is applied to the tip electrode, and current flows through the media that surrounds it, i.e., blood and tissue, toward the reference electrode. The distribution of current depends on the amount of electrode surface in contact with the tissue as compared to blood, which has a higher conductivity than the tissue. Heating of the tissue occurs due to its electrical resistance. The tissue is heated sufficiently to cause a lesion. Heating of the electrode results from conduction from the heated tissue. While the blood circulating around the ablation electrode tends to cool it, a stagnant area between the electrode and the tissue may be heated to such a temperature that a thin, transparent coating of blood protein forms on the surface of the tip electrode. This causes an impedance rise. When this occurs, the catheter must be removed and the tip electrode cleaned.
When RF current is applied to an ablation electrode in good contact with the endocardium to create a lesion, the temperature of the endocardium drops off very rapidly with distance from the electrode. The resulting lesion tends to be hemispherical, usually about 6 mm in diameter and about 3 to 4 mm deep.
When a tip electrode is irrigated, e.g., with room temperature saline, the tip electrode is cooled by the flow of saline through it and the surface of the electrode is flushed. Because the strength of the RF current is no longer limited by the interface temperature, current can be increased. This results in lesions which tend to be larger and more spherical, usually measuring about 10 to 12 mm.
The present invention provides a steerable catheter having an irrigated tip that is particularly useful in ablation procedures. The catheter comprises a catheter body having an outer wall, proximal and distal ends, and a single lumen extending therethrough. A control handle is fixedly attached to the proximal end of the catheter body. A tip section is fixedly attached to the distal end of the catheter body. The tip section comprises a flexible tubing, preferably more flexible than the catheter body, that has at least two lumens, and preferably three lumens, extending therethrough. A tip electrode is fixedly attached to the distal end of the tip section. The tip electrode has at least one fluid passage therethrough.
An infusion tube having proximal and distal ends extends through the lumen in the catheter body. The distal end of the infusion tube is in open communication with the proximal end of the fluid passage in the tip electrode so that fluid can flow through the infusion tube, into the blind hole in the tip electrode and out to the outer surface of the tip electrode. The fluid can pass through the tip electrode in a number of ways. For example, the fluid passage may have a plurality of branches extending to the outer surface of the tip electrode. Alternatively, the tip electrode may be sufficiently porous to allow fluid to pass from the proximal end of the tip electrode to the outer surface of the tip electrode.
The infusion tube may comprise one or more segments over the length of the catheter. In a preferred embodiment, the distal end of one infusion tube segment extends from the proximal end of the catheter body, through the catheter body and into the lumen in the tip section that is in fluid communication with the fluid passage in the tip electrode. A second infusion tube segment extends from the proximal end of that lumen in the tip section into the fluid passage in the tip electrode. Fluid can flow from the first infusion tube segment in the catheter body, into the lumen in the tip section, into the second infusion tube segment, into the fluid passage of the tip electrode, and to the outer surface of the tip electrode. Alternatively, a single infusion tube segment may extend through the catheter body and through a lumen in the tip section and may be anchored at its distal end in the fluid passage in the tip electrode.
The proximal end of the infusion tube preferably terminates in a luer hub. The proximal end of the infusion tube can extend out the proximal end of the control handle or out the side of the catheter body.
The catheter further comprises a means for deflecting the tip section. Preferably the control handle comprises a first member fixedly attached to the proximal end of the catheter body and a second member that is movable relative to the first member. A puller wire having a proximal end and a distal end extends from the control handle, through the catheter body and into an off axis lumen in the tip section. The distal end of the puller wire is fixedly secured within the tip section and the proximal end of the puller wire is fixedly secured to the second member of the control handle. Manipulation of the first member of the control handle relative to the second member of the control handle moves the puller wire relative to the catheter body, resulting in deflection of the tip section. In a preferred embodiment, a compression coil is located in the catheter body in surrounding relation to the puller wire.
The catheter preferably further comprises means for sensing the temperature of the tip electrode. A preferred temperature sensing means comprises a thermocouple formed by an enameled wire pair comprising a copper wire and a constantan wire. The wire pair extends through a lumen in the catheter body and a lumen in the tip section and is fixedly attached in a blind hole in the tip electrode.
In a particularly preferred embodiment, the catheter also contains an electromagnetic mapping sensor in the distal portion of the tip section for producing electrical signals indicative of the location of the electromagnetic mapping sensor within the heart. A sensor cable is electrically attached to the electromagnetic mapping sensor, extends through a lumen in the tip section, through the lumen in the catheter body and into the control handle. The proximal end of the sensor cable is connected to a circuit board, preferably within the handle, which is electrically connected to a suitable computer imaging system. In a preferred embodiment, a tubular housing is fixedly attached to the proximal end of the tip electrode for housing part of the electromagnetic sensor. The proximal end of the tubular housing is fixedly attached to the distal end of the flexible tubing of the tip section.